[CMake] Generated file and parallel build.

[Brad King]

Óscar Fuentes wrote:
> Several libraries depends on a generared header file. For enabling
> parallel builds I need to state that dependency, and I do it with
> set_source_files_properties. This happens inside a macro:
> 
> macro(add_llvm_library name)
>   if( LLVM_SOURCE_COMMON_DEPENDS )
>     set_source_files_properties( ${ARGN}
>       PROPERTIES OBJECT_DEPENDS ${LLVM_SOURCE_COMMON_DEPENDS}
>       )
>   endif( LLVM_SOURCE_COMMON_DEPENDS )
>   add_library( ${name} ${ARGN} )
> ....
> 
> where LLVM_SOURCE_COMMON_DEPENDS contains the name of the custom target
> that is used to trigger the custom command that generates the file:

You're mixing up file-level dependencies with target-level dependencies.
 The OBJECT_DEPENDS property only specifies file-level dependencies.  I
see its documentation is lacking.  I'll commit improved documentation
for it.  The add_dependencies command is used to create extra
inter-target dependencies:

macro(add_llvm_library name)
  add_library(${name} ${ARGN})
  add_dependencies(${name} ${LLVM_SOURCE_COMMON_DEPENDS})
  ....
endmacro()

Just make sure the LLVM_SOURCE_COMMON_DEPENDS variable contains only
target names and not files.

> add_custom_command(OUTPUT ${path_to_intrinsics_gen}
>   COMMAND tblgen -gen-intrinsic ... -o ${path_to_intrinsics_gen}
>   DEPENDS tblgen
>   COMMENT "Building intrinsics.gen...")
> 
> add_custom_target(intrinsics_gen ALL
>   DEPENDS ${path_to_intrinsics_gen})
> 
> set(LLVM_SOURCE_COMMON_DEPENDS ${LLVM_SOURCE_COMMON_DEPENDS} intrinsics_gen )

This is correct.

-Brad